A New Aspect of the Origin of Plasma Turbulence Driven by Field-Aligned Velocity Shear

1)提出了一种改进的等离子体合成方法，以主动控制磁场中的离子流能量，其中相同直径的离子和电子发射器相对地设置在圆柱形机器端部，并且离子发射器同心地分段成三个部分。当分段离子发射器的每个部分被单独偏置在高于等离子体电势的正值时，在径向均匀的等离子体电势中产生具有径向不同能量的场对准离子流。2）相邻层之间的这种离子漂移差异，或场对准离子流速度的径向跳跃被发现引起几种类型的低频不稳定性。一个是在径向中心附近观察到的，在那里密度分布几乎是均匀的。这种不稳定性是局部的流速跳跃的区域周围，和波动幅度变得很大时，两个电极之间的流速差增加。因此，这种不稳定性被认为在某种程度上与Kelvin-Helmholtz不稳定性有关。4）对于较大的流速梯度，在密度梯度相对较大的区域观察到另一种不稳定性。发现这种不稳定性的频率是电子-抗磁漂移频率和由离子流速决定的频率之和。因此，这种不稳定性似乎与电子漂移和离子声耦合波有关，这在传统的等离子体中还没有争论过。

1) A modified plasma-synthesis method is developed in order to actively control an ion flow energy in a magnetic field, where ion and electron emitters of the same diameter are oppositely set at cylindrical machine ends and the ion emitter is concentrically segmented into three sections. The field-aligned ion flows with radially-different energies are generated in a radially-uniform plasma potential when each section of the segmented ion emitter is individually biased at a positive value above the plasma potential.2) This ion drift difference between adjacent layers, or a radial jump of the field-aligned ion flow velocity is found to give rise to several types of low-frequency instabilities.3) One is observed around the radial center where the density profile is almost uniform. This instability is localized around the region of the flow-velocity jump, and the fluctuation amplitude becomes large when the flow-velocity difference between the two electrodes increases. Thus, this instability is considered to be related to the Kelvin-Helmholtz instability to some extent.4) For the larger flow-velocity gradient, another is observed in the region where the density gradient is relatively large. It is found that the frequency of this instability is the sum of the electron-diamagnetic drift frequency and the frequency which is determined by the ion flow-velocity. Thus, this instability appears to be related to the electron-drift and ion-acoustic coupled wave, which has not been argued in the conventional plasma.